There is a vertically aligned rectangle. The left and right sides are longer than the top/bottom sides. In the top right corner there is a small right triangle built into the rectangle, creating a diagonal line in place of part of the top and right sides. In the middle of the rectangle are the letters 'HTML'

This is the HTML Filetype icon for Windows 10. Here we go. Optimized for 32x32 px, these are the simplest icons in the line style. Downloadable formats are PNG and SVG, among others. Icons8 icon pack is unique in providing a huge number of icons designed by the same team of four designers who create the new icons every working day in the same style and with the same quality. Same cool as the Bat Face, huh.